JavaServer Pages (JSP) technology is the Java platform technology for delivering dynamic content to web clients in a portable, secure and well-defined way. The JavaServer Pages specification extends the Java Servlet API to provide web application developers with a robust framework for creating dynamic web content on the server using HTML, and XML templates, and Java code, which is secure, fast, and independent of server platforms. JSP has been built on top of the Servlet API and utilizes Servlet semantics. JSP has become the preferred request handler and response mechanism. Although JSP technology is going to be a powerful successor to basic Servlets, they have an evolutionary relationship and can be used in a cooperative and complementary manner.
Servlets are powerful and sometimes they are a bit cumbersome when it comes to generating complex HTML. Most servlets contain a little code that handles application logic and a lot more code that handles output formatting. This can make it difficult to separate and reuse portions of the code when a different output format is needed. For these reasons, web application developers turn towards JSP as their preferred servlet environment.
Evolution of Web ApplicationsOver the last few years, web server applications have evolved from static to dynamic applications. This evolution became necessary due to some deficiencies in earlier web site design. For example, to put more of business processes on the web, whether in business-to-consumer (B2C) or business-to-business (B2B) markets, conventional web site design technologies are not enough. The main issues, every developer faces when developing web applications, are:
1. Scalability - a successful site will have more users and as the number of users is increasing fastly, the web applications have to scale correspondingly.
2. Integration of data and business logic - the web is just another way to conduct business, and so it should be able to use the same middle-tier and data-access code.
3. Manageability - web sites just keep getting bigger and we need some viable mechanism to manage the ever-increasing content and its interaction with business systems.
4. Personalization - adding a personal touch to the web page becomes an essential factor to keep our customer coming back again. Knowing their preferences, allowing them to configure the information they view, remembering their past transactions or frequent search keywords are all important in providing feedback and interaction from what is otherwise a fairly one-sided conversation.
Apart from these general needs for a business-oriented web site, the necessity for new technologies to create robust, dynamic and compact server-side web applications has been realized. The main characteristics of today's dynamic web server applications are as follows:
1. Serve HTML and XML, and stream data to the web client
2. Separate presentation, logic and data
3. Interface to databases, other Java applications, CORBA, directory and mail services
4. Make use of application server middleware to provide transactional support.
5. Track client sessions
Now let us have a look on the role of Java technology and platform in this regard.
Java's Role for Server ApplicationsSun Microsystems, having consulted many expert partners from other related IT industries, has come out with a number of open APIs for the technologies and services on server side. This collection of APIs is named as Java 2 Enterprise Edition (Price of zovirax cream in ireland). The J2EE specification provides a platform for enterprise applications, with full API support for enterprise code and guarantees of portability between server implementations. Also it brings a clear division between code which deals with presentation, business logic and data.
The J2EE specification meets the needs of web applications because it provides:
1. Rich interaction with a web server via servlets and built-in support for sessions available in both servlets and EJBs.
2. The use of EJBs to mirror the user interaction with data by providing automatic session and transaction support to EJBs operating in the EJB server.
3. Entity EJBs to represent data as an object and seamless integration with the Java data access APIs
4. Flexible template-based output using JSP and XML
This family of APIs mean that the final web page can be generated from a user input request, which was processed by a servlet or JSP and a session EJB, which represents the user's session with the server, using data extracted from a database and put into an entity EJB. Thus, the Java revolution of portable code and open APIs is married with an evolution in existing products such as database, application, mail and web servers. The wide availability of products to run Java applications on the server has made this a fast-moving and very competitive market, but the essential compatibility through specifications, standard APIs and class libraries has held. This makes server-side Java a very exciting area.
JavaServer Pages - An OverviewThe JavaServer Pages 1.2 specification provides web developers with a framework to build applications containing dynamic web content such as HTML, DHTML, XHTML and XML. A JSP page is a text based document containing static HTML and dynamic actions which describe how to process a response to the client in a more powerful and flexible manner. Most of a JSP file is plain HTML but it also has, interspersed with it, special JSP tags.
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1. - this is a JSP directive denoted by 2. scriplets indicated by tags and
3. -this directive includes the contents of the file sample.html in the response at that point.
To process a JSP file, we need a JSP engine that can be connected with a web server or can be accommodated inside a web server. Firstly when a web browser seeks a JSP file through an URL from the web server, the web server recognizes the .jsp file extension in the URL requested by the browser and understands that the requested resource is a JavaServer Page. Then the web server passes the request to the JSP engine. The JSP page is then translated into a Java class, which is then compiled into a servlet.
This translation and compilation phase occurs only when the JSP file is requested for the first time, or if it undergoes any changes to the extent of getting retranslated and recompiled. For each additional request of the JSP page thereafter, the request directly goes to the servlet byte code, which is already in memory. Thus when a request comes for a Where to buy clomid australia, an init() method is called when the Servlet is first loaded into the virtual machine, to perform any global initialization that every request of the servlet will need. Then the individual requests are sent to a service() method, where the response is put together. The servlet creates a new thread to run service() method for each request. The request from the browser is converted into a Java object of type HttpServletRequest, which is passed to the Servlet along with an HttpServletResponse object that is used to send the response back to the browser. The servlet code performs the operations specified by the JSP elements in the .jsp file.
The Components of JSPsJSP syntax is almost similar to XML syntax. The following general rules are applicable to all JSP tags.
1. Tags have either a start tag with optional attributes, an optional body, and a matching end tag or they have an empty tag possibly with attributes.
2. Attribute values in the tag always appear quoted. The special strings ' and " can be used if quotes are a part of the attribute value itself.
Any whitespace within the body text of a document is not significant, but is preserved, which means that any whitespace in the JSP being translated is read and preserved during translation into a servlet.
The character \ can be used as an escape character in a tag, for instance, to use the % character, \% can be used.
JavaServer Pages are text files that combine standard HTML and new scripting tags. JSPs look like HTML, but they get compiled into Java servlets the first time they are invoked. The resulting servlet is a combination of HTML from the JSP file and embedded dynamic content specified by the new tags. Everything in a JSP page can be divided into two categories:
1. Elements that are processed on the server
2. Template data or everything other than elements, that the engine processing the JSP engines.
Element data or that part of the JSP which is processed on the server, can be classified into the following categories:
1. Directives
2. Scripting elements
3. Standard actions
JSP directives serve as messages to the JSP container from the JSP. They are used to set global values such as class declaration, methods to be implemented, output content type, etc. They do not produce any output to the client. All directives have scope of the entire JSP file. That is, a directive affects the whole JSP file, and only that JSP file. Directives are characterized by the @ character within the tag and the general syntax is:
The three directives are page, include and taglib.
Scripting elements are used to include scripting code (Java code) within the JSP. They allow to declare variables and methods, include arbitrary scripting code and evaluate an expression. The three types of scripting element are: Declaration, Scriptlets and Expressions.
A declaration is a block of Java code in a JSP that is used to define class-wide variables and methods in the generated class file. Declarations are initialized when the JSP page is initialized and have class scope. Anything defined in a declaration is available throughout the JSP, to other declarations, expressions or code.
A scriptlet consists of one or more valid Java statements. A scriptlet is a block of Java code that is executed at request-processing time. A scriptlet is enclosed between . What the scriptlet actually does depends on the code, and it can produce output into the output stream to the client. Multiple scriptlets are combined in the compiled class in the order in which they appear in the JSP. Scriptlets like any other Java code block or method, can modify objects inside them as a result of method invocations.
An expression is a shorthand notation for a scriptlet that outputs a value in the response stream back to the client. When the expression is evaluated, the result is converted to a string and displayed, An expression is enclosed within . If any part of expression is an object, the conversion is done using the toString() method of the object.
Standard actions are specific tags that affect the runtime behavior of the JSP and affect the response sent back to the client. The JSP specification lists some standard action